Computer security is fast becoming an important issue. With the proliferation of computers and computer networks into all aspects of business and daily life—financial, medical, education, government, and communications—the concern over secure file access is growing. Using passwords is a common method of providing security. Password protection and/or combination type locks are employed for computer network security, automatic teller machines, telephone banking, calling cards, telephone answering services, houses, and safes. These systems generally require knowledge of an entry code that has been selected by a user or has been configured in advance.
Pre-set codes are often forgotten, as users have no reliable method of remembering them. Writing down the codes and storing them in close proximity to an access control device (i.e. a combination lock) results in a secure access control system with a very insecure code. Alternatively, the nuisance of trying several code variations renders the access control system more of a problem than a solution.
Password systems are known to suffer from other disadvantages. Usually, passwords are specified by a user. Most users, being unsophisticated users of security systems, choose passwords which are relatively insecure. As such, many password systems are easily accessed through a simple trial and error process.
A security access system that provides substantially secure access and does not require a password or access code is a biometric identification system. A biometric identification system accepts unique biometric information from a user and identifies the user by matching the information against information belonging to registered users of the system. One such biometric identification system is a fingerprint recognition system.
Various optical devices are known which employ prisms upon which a finger whose print is to be identified is placed. The prism has a first surface upon which a finger is placed, a second surface disposed at an acute angle to the first surface through which the fingerprint is viewed and a third illumination surface through which light is directed into the prism. In some cases, the illumination surface is at an acute angle to the first surface, as seen for example, in U.S. Pat. Nos. 5,187,482 and 5,187,748. In other cases, the illumination surface is parallel to the first surface, as seen for example, in U.S. Pat. Nos. 5,109,427 and 5,233,404. Fingerprint identification devices of this nature are generally used to control the building access or information-access of individuals to buildings, rooms, and devices such as computer terminals.
One of the problems associated with fingerprint sensors concerns the reliable and accurate transformation of the ridge-and-valley pattern of the fingertip into electrical or optical signals to be stored in a digital format. Optical systems as described above, for example using a prism, require sophisticated equipment and tend to be bulky and costly.
In an attempt to overcome some of the limitations and disadvantages of using optical systems based on illumination of the finger tip, U.S. Pat. No. 4,353,056 in the name of Tsikos issued Oct. 5, 1982, discloses an alternative kind of fingerprint sensor that uses a capacitive sensing approach. The described sensor has a two dimensional, row and column, array of capacitors, each comprising a pair of spaced-apart electrodes, carried in a sensing member and covered by an insulating film. The sensors rely upon deformation to the sensing member caused by a finger being placed thereon so as to vary locally the spacing between capacitor electrodes, according to the ridge/trough pattern of the fingerprint, and hence, the capacitance of the capacitors. In one arrangement, the capacitors of each column are connected in series with the columns of capacitors connected in parallel and a voltage is applied across the columns. In another arrangement, a voltage is applied to each individual capacitor in the array. Sensing in the respective two arrangements is accomplished by detecting the change of voltage distribution in the series connected capacitors or by measuring the voltage values of the individual capacitances resulting from local deformation. To achieve this, an individual connection is required from the detection circuit to each capacitor.
In yet another attempt to improve upon deficiencies and limitations of the aforementioned and other prior art, a further contact imaging device is described in U.S. Pat. No. 5,325,442 in the name of Knapp, issued Jun. 28, 1994. Knapp describes making a capacitance measuring imaging device in the form of a single large active matrix array involving deposition and definition by photolithographic processes of a number of layers on a single large insulating substrate. Electrodes and sets of address conductors formed of metal and field effect transistors are formed as amorphous silicon or polycrystalline silicon thin film transistors (TFTs) using an appropriate substrate of, for example, glass or quartz.
A fingerprint sensing device and recognition system that includes an array of closely spaced apart sensing elements each comprising a sensing electrode and an amplifier circuit is described in U.S. Pat. No. 5,778,089 in the name of Borza, issued Jul. 7, 1998. The device is used to sense electrical charge on a fingertip and obviates the need to pre-charge the sensing electrode. The device may be constructed with a single die or with multiple dies.
It is a disadvantage of prior art fingerprint sensing devices that when used, the user leaves a latent fingerprint, similar to the type of fingerprints used by police to identify suspects at crime scenes. Thus, it is a problem that an unauthorized person can place a piece of paper over, for example, an optical fingerprint imager and the device will image the latent fingerprint and falsely identify the unauthorized person.
U.S. Pat. No. 6,084,977, issued to Borza Jul. 4, 2000, provides a method for detecting a record-playback attack in which an exact copy of a previously provided fingerprint is provided to a fingerprint-imaging device. An example of such an exact copy is a latent fingerprint left on the imaging platen. Unfortunately, an unauthorized individual could simply replace an existing biometric input device with a different biometric input device having a latent fingerprint image on a platen surface thereof. The system does not recognize the latent fingerprint image as such because an exact copy, used previously to authenticate a user, does not exist in the system memory. Of course, a fingerprint recognition system that includes a plurality of remotely located terminals, each terminal in communication with a central information database, is not necessarily susceptible to this particular limitation.
It is a further limitation of the prior art that, by altering a latent fingerprint slightly and in a manner that does not affect authentication, an unauthorized user will be falsely authenticated. For instance, the unauthorized user wipes away or smudges a portion of the fingerprint around the periphery thereof, but leave the core intact for authentication purposes. As such, the latent fingerprint is other than an exact copy of a previously imaged fingerprint, and authentication is still possible because the core is intact.
It would be advantageous to provide a method for preventing use of latent fingerprints in user authentication for contact imaging devices. In particular, it would be advantageous to provide a method, which method recognizes a latent fingerprint in dependence upon a same region of a fingerprint that is used to authenticate the individual providing the fingerprint.